Many fields use adhesives, glues, and plastics which must be cured before setting. The curing process often results in shrinkage of the material, which in turn causes stresses to arise within the material and the substrate to which the material is bonded.
For example, in the field of dentistry, dental restoration procedures often require various resin-containing materials, such as composites and adhesives, to be filled into a tooth cavity or area being repaired. The material is then cured using a hand tool which emits light through a bundle of optic fibers to result in a focused light output. The material is cured by polymerization resulting from the light exposure.
However, shrinkage of the restorative material used to fill the cavity can create stresses which may lead to premature failure or otherwise necessitate repair. Development of adhesives and polymers which undergo less volumetric change, or development of curing methods which relieve stress, are therefore advantageous in the development of new storage materials. A key to the development of such materials is the ability to measure small changes in volume. Present methods used to measure volumetric changes include water or mercury dilatometers, or methods which measure a change in one dimension and try to deduce volumetric change therefrom.
Water and mercury dilatometry operate by measuring the amount of water or mercury which is displaced by the sample volume within a sample chamber. The volume of mercury or water is determined by weighing the displaced water or mercury. The accuracy of these techniques and instruments require precisely controlling temperature, precisely controlling the chamber volume from which the water or mercury are displaced, and precisely weighing the displaced mercury or water. Errors can be introduced into the measuring process at any or all of the steps. In addition, such instruments are time consuming to use and, due to the many steps required to obtain a measurement, can suffer from operator bias. Sample interactions between the displacement fluid and the sample can also affect accuracy. For example, polymers used for restorative dentistry may absorb water and may expand as a result. Also, due to the time consuming nature of each measurement, the number of measurements which can be practically made by a researcher is limited.
Controlling the manner in which the curing process is conducted may also relieve stresses within the material boundaries. For example, the manner in which light is applied to light-cured restorative materials in dentistry may relieve the stress between the adhesive and the tooth. Testing this hypothesis, however, requires an instrument which can reveal not only the amount of volume change, but also the location or locations at which the sample volume has changed. It would also be helpful to know the portion of the sample which changed volume first.